QUESTION:  
Why is Martian soil so important?

ANSWER from Ted Roush on January 31, 1997:
Why is soil on the Earth important?

On the Earth we know that different soils form in different climates.
This allows geologists to identify how climates might have been
different in the past.  We also know that different soils form from
different starting materials on the Earth.  This allows geoscientists
to identify the different starting materials.  Understanding what
these starting materials were provides geoscientists with an idea of
what materials are found beneath the Earth's crust.  Like on the Earth,
such knowledge about the martian soil can provide direct information 
regarding the activity and evolution of the martian atmosphere and
may provide information regarding the interior of Mars.  With such
knowledge planetary scientists can compare the atmosphers, surfaces,
and interiors of various planets in the solar system and perhaps
learn more about how our solar system formed and evolved.

On the Earth different materials are used as resources to support 
human existance.  Rocks and soils can be used as construction 
materials.  For example, some soils are turned into bricks that can
be used to provide humans with protection from the weather.  On Earth
we extract valuable resources from rocks and soils and we grow food,
mostly in soils, to sustain life.  Thus, The martian soil represents 
a valuable resource that future travellers to the red planet might
use.  For example, the soil could provide an insulating and
protective layer for astronauts living on the surface of Mars.  If 
the soil contains trapped water that could be extracted, then it 
could provide both a source of water, necessary for sustaining a
human colony on Mars, and fuel, necessary fortransportation on Mars.
The soil would be an important material for growing food to help 
support the presence of a human colony on Mars.